Unhextrium
Unhextrium, Uht, is the temporary name for element 163. NUCLEA PROPERTIES Since at least two sets of predictions exist for location of the neutron dripline up to Z = 175(1),(2), the outer boundary derived in "The Final Element" (this wiki) is too crude to add anything to what is known about Uht. The inner boundary described in that wiki is more reliable. It indicates that Uht isotopes are possible within the band ranging from Uht 372 to Uht 559. (In this case Uht 559 may not be the actual upper bound. See "Unhexquadium", this wiki, for details.) All isotopes of Uht require at least 2.9 MeV of structural correction in order to survive long enough to beta-decay. We know little about structural correction values, except for predictions of shell closure locations. A neutron shell closure has been predicted at N = 370(2), which implies that Uht isotopes in the vicinity of Uht 533 may beta decay. A proton shell closure has also been widely predicted to occur at Z = 164, which may extend the range of beta-decaying Uht isotopes beyond what the neutron shell closure would cause. At least one model exists predicting the half-lives and decay modes for nuclides up to Z = 175 and N = 333(3), which includes isotopes Uht 496 and lighter. It is helpful to view p 18 of Ref. 3, which maps predicted half-lives of nuclides in this region, and p 15, which maps principal decay modes. Uht itself needs to be seen in context of the whole nuclear map of its surroundings. The map predicts a band of nuclides ranging from Uht 438 to Uht 472. As neutron count increases in this band, half-life increases, reaching a maximum which exceeds a second and may be as much as 1000 sec. Principal decay mode shifts from fission, to alpha emission, then to beta emission. This pattern is expected from a neutron shell closure at N = 308. However, there is also a band of comparatively stable alpha-decaying isotopes predicted to lie between Uht 473 and Uht 483 which do not appear to be stabilized by N = 308. A neutron shell closure has also been predicted to occur at N = 318(4) and a proton shell closure has been predicted at Z = 154(2). Uht 473 to Uht 482 may indicate effects of those two closures, as well as N = 308 and Z = 164. ATOMIC Several predictions for the ground state electron structure of Uht agree that it will have transition metal character, with 7d and 9s electrons available for bonding. Electrons in Uht can be described in terms of time-independent orbitals, but calculation of electron properties require that nuclear charge be distributed over the nucleus' actual volume. In addition, there is some chance that differing nuclear shapes may produce different electron configurations in different isotopes. (Different isotopes would be different elements in the chemical sense.) Except in the laboratory, Uht is found only in environments too hot for ordinary chemistry to occur. FORMATION Neutron capture cannot produce nuclides much larger than A = 500, since fission is expected even at the inner dripline above this point. As material originally from 800 – 1000 m deep within a neutron star is forced outward when the star disintegrates during a merger, large drops of nuclear matter located near the inner neutron dripline will probably appear. Where stabilized by around 3 MeV by the nearby presence of a shell closure, these drops may be beta-decaying nuclides, which can subsequently evolve toward higher Z until they reach nuclides which fission. Such a band, anchored by N = 370, may allow isotopes in the Uht 520 to Uht 560 range to form. Fission (especially from excited daughters) will compete with beta decay during evolution to Uht, which may greatly reduce the amount which forms. Fission and multinucleon transfer reactions occurring in the polar jets emanating from neutron stars and black holes may allow isotopes in the band Uht 375 to Uht 500 to form. Quantities produced in this way are tiny. REFERENCES 1. "Neutron and Proton Drip Lines Using the Modified Bethe-Weizsacker Mass Formula; D.N. Basu et al; Int.J.Mod.Phys.; arXiv:nucl-th/0306061; url: https://arxiv.org/abs/nucl-th/0306061 2. “Single Particle Levels of Spherical Nuclei in the Superheavy and Extremely Superheavy Mass Region”; H. Koura and S. Chiba; Journal of the Physical Society of Japan; DOI 10.7566/JPSJ.82.014201; Jan. 2013. 3. "Decay Modes and a Limit of Existence of Nuclei"; H. Koura; 4th Int. Conf. on the Chemistry and Physics of Transactinide Elements; Sept. 2011. 4. “The Highest Limiting Z in the Extended Periodic Table”; Y.K. Gambhir, A. Bhagwat, and M. Gupta; Journal of Physics G: Nuclear and Particle Physics. 42 (12): 125105. DOI:10.1088/0954 3899/42/12/ 125105. (01-02-20)